Load Power Factor

[Cerkit]

Hi,

I am struggling to see how I can plot a vector of a current for which the load is stated to have wattful and wattless components of 87% MW export and 50% MVAr import respectively.

Does anyone understand this?

Thanks

 

[pwrengrds]

If total is 100 MW's then exporting 87 MW's to the grid and 50 MVAR capacitive. (assuming capacitive is importing)
98.6 MVA, Power factor 0.88. I might be wattless though, David

 

[waross]

Your power triangle will have a base of 87 units, an altitude of 50 units and a hypotenuse of root (87[sup]2[/sup] + 50[sup]2[/sup]) units = 100.34 units or 100.34 MW. 100 MW, close enough.
Your power factor is 87 MW / 100.34 MVAR = 0.87 PF.
0.87 is the cosine of the phase angle, for your vector sketch.
Plus or minus depends on resolution of exporting and importing.
Inductive loads generally demand an import of both real and reactive power.
An exception may be a long, heavily loaded downhill conveyor that is back-feeding 87 MW while still drawing 50 MVAR of magnetizing current.
87 MW? That's around 90,000 HP
Scary big conveyor.
Your data is strange. The phase angle displacement will be as noted, direction to be determined.
Is this perhaps a Power Plant Exporting to a load?
I am not in disagreement with pwrengrds's numbers. Different rounding errors.
MVARs may be positive or negative which may lead to one man's importing of leading MVARs to be another man's exporting of lagging MVARs.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[davidbeach]

100 MVA, not 100 MW. Only 87 MW.

 

[rcw retired EE]

Draw your MW/ MVAr plot with MW on the x (horizontal) axis and MVAR on the y (vertical axis). MW out to the load is positive on the right half plane (right of y axis). MVAR's to the load is on the upper half plane (above x axis). MVAR's from the load is on the lower half plane.

Plot your operating point at 87 MW and - 50 MVAR. The vector from the origin to the operating point will be 100 MVA at -29.5 degrees (cos(29.4) = 0.87 ) The MVA vector also represents the current vector, assuming that the voltage is constant.

As others have implied, the positive and negative values depends on which side of the meter you are standing. Power out of a generator to the load is positive for the power producer, negative for the distribution utility when it takes the power and positive for the utility when it delivers the power to the customer. The customer usually considers positive power flow to be to the load.

 

[FreddyNurk]

I've definitely seen watt export var import before, although at about 100MVA the scale is way off what I'd seen. Lightly loaded longer distance overhead lines can often end up in this sort of situation, watts out to feed the load, but var import due to the distance and loading on the overhead lines.

I wouldn't consider the context in which I'd seen it typical or common though. I would imagine that for generating plant the numbers you describe would cause excitation issues too.

EDMS Australia

 

[cuky2000]

Below is an attent respond to your question with the normalized data provided (%MW & %MVAr).
As a general comment, the following applies:
1) The current direction in the power triangle is the same as to apparent total power.
2) The current magnitude could be determined if the system voltage information is available in the same bases as the %MW & %MVAr.
3) Export and import of active power (wattful) and reactive powers (wattless) components are indicated in the graph below
We hope this helps.

........